Ti/Pt/Au ohmic contacts to β-Ga2O3

Low-resistance and thermally stable ohmic contacts are essential for realizing high-performance β-Ga2O3 power devices. Although Ti/Au electrodes are widely used as conventional ohmic contacts, Ti–Au interdiffusion during high-temperature annealing remains a critical issue. Introducing a Pt diffusion barrier between Ti and Au is expected to suppress this interdiffusion and improve the thermal stability of the contacts. However, the effectiveness of the Pt layer has not been systematically established through a direct comparison of Ti/Pt/Au and Ti/Au electrodes. In this study, we systematically compared Ti/Pt/Au (30/20/70 nm) and Ti/Au (30/70 nm) ohmic electrodes on (001) β-Ga2O3 epiwafers annealed at temperatures (T) ranging from 400 to 600 °C. Both electrode stacks formed ohmic contacts at T ≥ 450 °C. At T ≥ 500 °C, however, the Ti/Pt/Au and Ti/Au electrodes exhibited distinctly different behaviors. The Ti/Pt/Au electrodes maintained their layered structures up to T = 550 °C and achieved a minimum specific contact resistivity of (7.17 ± 1.35) × 10−6 Ω cm2 at T = 550 °C, whereas the Ti/Au electrodes exhibited severe Ti–Au intermixing at T ≥ 500 °C and degraded electrical properties, consistent with the cross-sectional scanning transmission electron microscopy observations. This clear contrast demonstrates that the thin Pt layer served as an effective diffusion barrier, thereby improving the thermal stability of the electrodes and enabling higher-temperature annealing to achieve better contact properties.